1. Field of the Invention
The invention relates to a method for providing a plurality of mobile earth terminals (“METs”) random access to communication with one or more satellites, and more particularly, to a method for providing efficient communication between a plurality of METs and a constellation of low earth orbit satellites through the use of subbanding and the use of more than one message length.
2. Description of the Related Art
Numerous methods are known for providing random access to a communication satellite by a plurality of METs typically having “bursty” traffic. Bursty traffic is traffic that is intermittent in nature rather than continuous for extended periods of time. These systems only provide the MET communication access to the satellite when the MET has information to send. Such systems can be contrasted with those providing a cycle during which every possible sender has a certain access window. The complexities of providing an efficient process for random access communications increase significantly when the METs are communicating with a constellation of low earth orbit satellites.
For example, nations have varying regulatory requirements for such communications. In addition, some nations allow communication at frequencies at which another nation may prohibit commercial communications because the frequency is used for emergency, police or military communications. Low earth orbit satellites can have a large footprint that covers several nations simultaneously. Therefore, METs in different nations may try to access the same satellite at the same time. Thus, it would be desirable to provide a communication system wherein the satellites could process information received from a variety of different METs while simultaneously honoring the communication regulations of each of the nations.
Sending messages in a random access communication system requires some amount of overhead communication simply to request and establish the communication link between the MET and the satellite receiver. This is because the bursty nature of the traffic and the large number of METs make it impractical for every MET to have a fixed communication slot.
Sending multiple messages of the same predetermined length to convey a large amount of information increases the amount of overhead necessary as compared with the overhead required to send one message of increased length. Thus, it may seem that simply designing the system with an increased message length might be an effective solution. Increasing the predetermined message length of the system, however, often would be inefficient because many of the messages would not require this much capacity, thereby wasting capacity. Wasting capacity is costly, especially when other METs are waiting to send a message. Thus, it would be desirable to have a communication system that efficiently provides communication to a satellite by allowing METs to send messages of more than one length.